The present invention relates generally to delivery of digital information to subscriber premises and more particularly to providing this access without substantial new wiring expense.
The delivery of digital video services to the home represents one important aspect of the much publicized "information highway." These services include HDTV, video-on-demand (VOD), near-video-on-demand (NVOD) providing staggered program starting times, interactive video services (IVS), and other digital variants of conventional broadcast services.
One of the main obstacles to the introduction of these services is development of the necessary infrastructure for delivering digital video information to the subscribers' premises. Video services, even with the use of modern compression standards such as MPEG-1 and MPEG-2, intrinsically require large bandwidths. Somehow an infrastructure must be constructed to distribute the necessary signals to individual subscriber premises. At a minimum, each subscriber should be able to select from among numerous digital video programs as can be done now with analog broadcast television.
Various solutions have been proposed. In one scheme, the digital data are distributed via an asynchronous transfer mode (ATM) network to each subscriber's premises. The physical medium of the ATM network may be implemented in more than one way. One way is to lay optical fiber to each home. Alternatively, fiber may be laid up to the curb, from which point a coaxial cable can relay the ATM cells. The advantages of this technique are the low latency and flexibility of the ATM technology and a large bidirectional bandwidth sufficient to distribute numerous interactive digital video programs. Nonetheless, this approach is practically infeasible today since the cost of laying fiber or coaxial cable to each home is prohibitive. Additionally, the time required to deploy such an infrastructure over a large geographic area makes the scheme even more unattractive.
An alternative scheme is the so-called hybrid fiber coax (HFC) scheme. The HFC scheme provides a two-level network. At the higher level, optical fibers are used to distribute digital information to a plurality of Cable Headends or Host Digital Terminals (HDT). Each Headend or HDT in turn distributes information to multiple hybrid fiber coaxial cables, each of which serves several hundred subscriber units in a bus/loop architecture. The return channel over the coaxial cable is also shared by multiple subscriber units by employing Time Division Multiplexing (TDM). Again, for those network providers that do not already have such an infrastructure installed, costs are prohibitive because coaxial cable must be brought to each home. Furthermore, the use of TDM coupled with highly limited bandwidth gives rise to a large latency in the return channel. Network security is another drawback of the HFC architecture as several users share a single coaxial cable, a particular concern for interactive services that may require transmission of a subscriber's private information.
Other schemes take advantage of the existing telephone network by using ADSL technology to transfer high data rate information, such as video, over existing telephone company twisted pair lines to subscriber premises. Optical fiber may be used to transfer digital information to the telephone company central office or to a curbside interface where the twisted pair lines begin. The latter architecture is commonly referred to as Fiber-To-The-Curb (FTTC). Alternatively, fiber may be deployed till the basement of a large building, from which point existing twisted pair lines can establish connection with each subscriber. Such an architecture is commonly referred to as Fiber-To-The-Building (FTTB). The disadvantage of this approach is that ADSL provides insufficient bandwidth. Most current ADSL trials carry only 1.5 or 2 Mb/s over twisted pair. Laboratory demonstrations have shown that in the next few years cost effective solutions that provide up to 25 Mb/s may be possible, but even this would be insufficient to provide a broadcast or NVOD service with an acceptable number of service selections. Approaches which bring fiber to the curb carry the added cost of laying the fiber.
Prior art digital data delivery schemes that use relatively narrow bandwidth connections to the subscriber premises require point-to-point sessions between the ultimate server and subscriber unit. This is because the narrow bandwidth link that is closest to the subscriber permits only a point-to-point connection if the desired service quality is expected to be reasonable. These point-to-point sessions waste bandwidth since the server must separately transmit to multiple subscriber units requesting the same program. If the user wishes to switch channels, there is significant extra latency resulting from the need to end the previous point-to-point session before beginning a new one. Furthermore, the network and server hardware needed to accommodate point-to-point sessions is particularly complex and expensive.